Transcript DRILLING FLUID SEPARATION & IT’S ENVIRONMENTAL ISSUE

DRILLING FLUID SEPARATION & IT’S
ENVIRONMENTAL ISSUE
DESALEGN YESHITILA
NUGROHO ADI SASONGKO
1. Solid control history
2. Functions of drilling fluid
3. Solids control equipment
4. Environmental impacts
History of solid control
Drilling fluid maintenance cost, clean up &
disposal cost as well as the over all cost of
boring, can be reduced dramatically when
proper solids control techniques are
utilized. These facts were recognized in the
oil industry in the late 1800’s. When open
earthen pits we used to separate the
cuttings from the borehole. This was
accomplished by a series of weirs and
settling pits that allowed the solids to
naturally settle out by using gravity. The
clean mud then flowed into a suction pit to
be re-pumped down hole. This was the first
solids control technique ever used
Functions of drilling mud
to control subsurface pressures,
lubricate the drill bit, stabilize the well
bore, and carry the cuttings to the
surface, among other functions. Mud is
pumped from the surface through the
hollow drill string, exits through
nozzles in the drill bit, and returns to
the surface through the annular space
between the drill string and the walls
of the hole
Benefits of low solids in drilling
Mud
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Increased drilling penetration
Increase bit or back reamer life
Reduce mud cost
Reduce triplex mud pump, mud
motor & surface equipment
maintenance cost.
Reduced clean up & haul off or
disposal cost
Mud Circulating System
Solids removal theory
Drilling fluid and equipment
maintenance cost can decrease
greatly when proper solids control
practices are utilized. From a fluid
control stand point it would be
desirable in most cases to remove all
drilled solids. Although this is
possible, it would be cost prohibitive.
The goal of a solids control system is
to achieve the balance between
mechanical solids separation and
dilution that will result in drill solids
being maintained at an acceptable
level with a minimum of cost
Particle size and effects
- Drilled solids are those particles that enter the mud system in the form of cuttings from the
bit or back reamer or from borehole debris. These solids vary in size from less than one micron
& larger depending on the carrying capabilities of the drilling fluid.
- Drilling fluid is classified as water base utilizing water as the liquid phase. The solid phase of
any drilling fluid is either commercial solids or drilled solids. Most commercial solids such as
bentonite have a relative particle size of less than one micron. (.000039 inches).
Methods of
controlling solids
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Mechanical treatment
Chemical treatment
Dilution of mud with
water
Discard mud & mix new
mud
Mechanical separation basics
Mechanical separation equipment employs mass differences, size
differences or a combination of both to selectively reject undesirable
solids and retain desirable drilling fluid. The desanders and desilters
utilize centrifuge force and mass difference between the solids density
and liquid density for solids removal. The shale shakers employ a
vibrating screen of various micron-sized differences.
Basic
Equipment of
Mud Solid
Control
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Shale shaker
Desander
Desilter
Hydrocyclone
Mud cleaner
Shale shaker
One method of removing solids from drilling mud is to pass the mud over the surface
of a vibrating screen. Particles smaller than the openings in the screen pass through
the holes of the screen along with the liquid phase of the mud. Particles too large to
pass through the screen are thereby separated from the mud for disposal. Basically,
a screen acts as a “go-no-go” gauge: Either a particle is small enough to pass
through the screen or it is not.
Decanter
Hydrocyclones
Hydrocyclones are simple mechanical
devices, with out moving parts, designed
to speed up the settling process. Feed
pressure is transformed into centrifugal
force inside the cyclone or cone to
accelerate particle settling in accordance
with Stoke’s Law #1. In essence, a
cyclone is a miniature settling pit which
alloys very rapid settling of solids under
controlled conditions.
Environmental
Issue of drill cutting
During drilling operations, two types of drilling waste are created:
Cuttings (rock mass) and useddrilling mud. Drilling fluid will always be attached to cuttings. The
industry uses three types of drilling
fluids, all with different technical and environmental properties. The authorities’ requirements
related
to the disposal of waste are linked to the following properties:
Oil-based drilling fluids (OBM): Have in most cases the best technical properties. The authorities
do not permit the discharge of OBM and cuttings drilled with oil-based drilling fluids. Cuttings and
fluids are taken to shore.
Water-based drilling fluids (WBM): The authorities permit the discharge of used drilling fluid and
cuttings upon application.
Synthetic drilling fluids (SBM): Based on ether, ester or olefin. They have technical properties that
are similar to oil-based drilling fluids in many ways. Discharge of used SBM is not permitted, but
the discharge of cuttings may be permitted upon application.
The use of water-based drilling fluids has increased by 20 per cent from 2005. There have not been
any reports of the use of synthetic drilling fluid in 2006, while the use of oil-based drilling fluids has
been reduced by 16 per cent.
Treatment of drill cutting
1. Discharge (Offshore)/Disposal to sea - If the cuttings are considered
low environmental risk and depending on local regulations, they can be
disposed into the sea in certain regions. However, most require some pretreatment to reduce the oil-on-cuttings to less than 6.9% by volume on a
wet weight basis.
2. Transportation to Shore
3. Injection - In the injection process, the cuttings are converted into slurry,
which is then pumped into a receiving formation at pressures exceeding
the fracture gradient.
Environmental Issue
The dryness of the cuttings aids disposal or re-use.
Drill Cutting Transportation
In previous picture is shown the new designed platform supply vessel ST216 with 8
integrated structural tanks under deck for drill cutting of total abt. 430 m3. Number
of tanks can be adjusted to suit actual capacity requirements.
To day handling of drill cutting give a potential hazard to following:
* Possible pollution to sea through disposal on sea bed
* Potential spillage to sea
* Safety risk for personnel through extensive manual handling and lifting
operations.
* Safety risk to personnel and vessel in cases where transported DC may be
classified as hazardous cargo containing low flash point substances.
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